Don't forget that you can add what you are looking for as a key word.
You can add these words to your search:
Try searching with a name and add key words such as "primary sources" or "letters"
Check out the Primary Sources Guide for tips about finding primary sources
Many libraries and archives will have a digital presence, use Google to help find them
Find books in the library's catalog (and remember to browse the shelves while you're up there!) Take advantage of the suggested readings, and additional sources at the ends of entries and chapters. If an author refers to another source, you can always track that one down as well!
Don't forget to explore your textbook for additional sources and suggested readings.